Protandry, a neuter phase, and unisexual umbels in a hermaphroditic, Neotropical vine ( Bomarea acutifolia , Alstroemeriaceae)

Protandry is a common form of dichogamy in species with hermaphroditic flowers, yet the temporal separation of male and female organs is rarely synchronized enough to prevent self‐pollination among flowers on the same plant. Here we report an unusual mechanism for synchronized protandry within umbels of Bomarea acutifolia , a hummingbird‐pollinated vine in Costa Rica. Flowers in the same umbel open over a period of several days and spend approximately 9 days in the male phase while the six anthers dehisce one by one. Each flower then enters a week‐long neuter phase during which the spent stamens move away from the elongating style and nectar production continues. This is followed by a short female phase when the stigma finally becomes receptive. The long neuter phase ensures that most umbels are temporally unisexual, thereby limiting opportunities for self‐pollination among flowers in the same umbel. A neuter phase has been reported in a few other dichogamous species, but to our knowledge this is the first description of a phase in which the flowers remain open and continue to provide nectar without dispersing or receiving pollen.